codecov: exclude generated files

Gogo generated boilerplate skews result. This
could probably be removed after Gogo is gone.

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

codecov.yml

@@ -10,3 +10,6 @@ coverage:
 
 github_checks:
   annotations: false
+
+ignore:
+  - "**/*.pb.go"